The application of Recycled Concrete Aggregate (RCA) for Hot Mix Asphalt (HMA) base layer aggregate

KSCE Journal of Civil Engineering (2011) 15(3):473-478DOI 10.1007/s12205-011-1155-3

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www.springer.com/12205

Highway Engineering

The Application of Recycled Concrete Aggregate (RCA) forHot Mix Asphalt (HMA) base Layer Aggregate

Yoon-Ho Cho*, Taeyoung Yun**, In Tai Kim***, Nyoung Rak Choi****

Received March 2, 2010/Accepted July 26, 2010

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Abstract

Recycled Concrete Aggregate (RCA) is different from natural aggregate because of RCA’s cement paste and contaminants thatcause low density and high porosity. In many cases, these properties of RCA that lead to poor engineering qualities are the majorreasons that RCA is not recommended as aggregate for Hot Mix Asphalt (HMA). In this research, the performance of HMA mixtureswith RCA is quantitatively evaluated using various tests to verify the applicability of RCA as aggregate for HMA material. For thisverification, the Indirect Tensile (IDT) strength test, Kim test, wheel tracking test, and tensile strength ratio test accompanied byfundamental material property tests were performed on asphalt mixtures with four types of aggregate blends. In addition, asphaltmixtures with RCA, whose binder contents were determined from the Superpave mix design method, were utilized and evaluatedagainst Marshall design criteria in order to effectively reflect both field specifications and field compaction conditions in SouthKorea. As a result of this study, it is observed that the study asphalt mixtures with RCA (Mixes II and III) show good performancecompared to the asphalt mixture with natural aggregate only (Mix I) in terms of indirect tensile strength ratio, deformation strength,rut depth, and IDT strength, whereas Mix IV, which consists of coarse and fine RCA, does not exhibit good performance. Byevaluating the Marshall test properties of each mixture, it is also concluded that the dynamic loading in the Marshall test compactionmethod possibly causes friction in the RCA of the asphalt mixtures and, therefore, leads to an underestimation of the engineeringproperties of HMA with RCA.Keywords: Recycled Concrete Aggregate (RCA), Hot Mix Asphalt (HMA) base material, Kim test, moisture susceptibility

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1. Introduction

From the viewpoint of environmental preservation and effec-tive use of resources, focus on recycling construction wastes hasincreased all over the world. In pavement engineering, studies ofthe utilization of Recycled Asphalt Pavement (RAP) aggregateand Recycled Concrete Aggregate (RCA) have been performedover the past twenty years and have utilized various testingprotocols (Kandhal et al., 1995; Sondag et al., 2002; Tam et al.,2004). In one of the early studies on recycled aggregate, Ramziet al. (1999) report that a blend of RAP and virgin materialsatisfactorily functions as a sub-base layer material. They re-searched the performance of mixtures with various RAP-virginproportions using test protocols such as physical, compaction,and California Bearing Ratio (CBR) tests, and observed that a60/40 RAP/virgin blend shows the best performance for sub-base layer material. Ramzi et al. also observed that a 10/90 RAP/virgin blend shows the best performance for base layer material.

Su et al. (2009) showed that recycled asphalt could achieveproperties similar to the virgin asphalt that guard against long-term aging. They evaluated the performance of the mixtures usingadvanced testing protocols, such as wheel tracking, raveling, andbending beam tests. Su et al. suggest recycled asphalt concretecontaining 40% RAP as a surface layer material for airportpavements.

Brandon et al. (2006) investigated the properties of RCA usingvarious laboratory tests and confirmed the possibility of usingdemolished concrete material. From other RCA studies (Poon etal., 2005; Park 2003), it was concluded that RCA mixed withvirgin aggregate is applicable for the base layer material.Paranavithana et al. (2006) also report encouraging results usingRCA for HMA from the resilient modulus test and creep test.However, they note the need to evaluate the resistance of themixtures to stripping in order to cover a wider range of per-formance of HMA with RCA.

*Member, Professor, Dept. of Civil and Environmental Engineering, Chung-Ang University, Seoul 156-756, Korea (E-mail: [email protected])**Member, Senior Researcher, Highway Research Division, Korea Institute of Construction Technology, Goyang 411-712, Korea (Corresponding Author,

E-mail: [email protected])***Member, Assistant Professor, Dept. of Transportation Engineering, Myongji University, Yongin 449-728, Korea (E-mail: [email protected])

****Research Assistant, Dept. of Civil and Environmental Engineering, Chung-Ang University, Seoul 156-756, Korea (E-mail: [email protected])

Yoon-Ho Cho, Taeyoung Yun, In Tai Kim, Nyoung Rak Choi

− 474 − KSCE Journal of Civil Engineering

2. Experimental Study

2.1 Material and Specimen FabricationFour types of mixtures with a Nominal Maximum Aggregate

Size (NMAS) of 25 mm are considered in this study. In order toevaluate the effect of aggregate size on the fundamental proper-ties of HMA mixtures, fine aggregate and coarse aggregateobtained from both natural crushed aggregate and RCA wereblended and are described in Table 1. For Mix I, only naturalaggregate was used, whereas natural aggregate and recycledaggregate were used respectively as coarse aggregate and fineaggregate for Mix II. All the mix types were mixed with PG64-22 binder, and the optimal binder content for each mix wasdetermined following the Superpave mix design method. The flator elongated particles in natural and recycled coarse aggregatesare determined according to KS F 2575 and ASTM D 4791 andthey are 19.91% and 16.78%, respectively. The absorption ratiosand densities of natural and recycled aggregate are determinedaccording to KS F 2503 and KS F 2504 and are shown in Table2. Fig. 1 shows the mix gradation chart for the aggregate struc-tures used for this study.

All mixtures except those used for the Marshall test werecompacted by a gyratory compacter to a diameter of 150 mm anda height of 170 mm after four hours of aging. To obtain speci-mens with uniform air void distribution, specimens were coredto a diameter of 100 mm and cut to a certain height based on the

testing protocol utilized. From the preliminary tests that usedvarious air void contents, it was found that the compacted cylin-drical mixture with an air void of 7.5% results in cored specimenswith an air void of 5.0±0.5, which is the requirement for asphaltmixtures used in base layers in South Korea. Meanwhile, thespecimens used for the Marshall test were compacted and testedaccording to the Marshall mix design protocol. It is beneficial toevaluate the performance of the mixtures, whose proportions aredetermined by the Superpave mix design method, against theMarshall criteria because in many countries, including SouthKorea, the specifications for the base layer material still recom-mend the Marshall mix design method. Fig. 2 presents the mea-sured air void distribution of each mixture compared to a targetair void of 5 percent.

2.2 Testing ProtocolsThe absorption ratios of the four mix types were compared to

evaluate the economic benefits and other properties of asphaltmixtures that use RCA. Four different tests were considered, asfollows: 1) the Marshall test and 2) IDT test were performed toevaluate the resistance of the mixture to cracking; and 3) the Kimtest and 4) wheel tracking test were performed to evaluate the rutresistance of the mixtures. The experimental protocols for thesetests are explained in the following sections.

2.3 Absorption TestThe maximum absorption of asphalt mixtures used for the base

layer in South Korea is 3%; the absorption test was performedaccording to ASTM C-127. All mix types, except for Mix IV,satisfy this criterion. Even though the absorption ratio of Mix IVis higher than that of the specification, other performance evalua-tion tests were still performed on Mix IV because the absorptionvalue was so close to 3% (3.1%), as shown in Table 3.

Table 1. Designation of Natural-Recycled Aggregate Blends

Mix I Mix II Mix III Mix IV

Coarse Aggregate ( > 4.75 mm) Natural Aggregate 100% Natural Aggregate 100% Recycled Aggregate 100% Recycled Aggregate 100%

Fine Aggregate ( < 4.75 mm) Natural Aggregate 100% Recycled Aggregate 100% Natural Aggregate 100% Recycled Aggregate 100%

Optimal Asphalt Content (%) 4.30 4.65 4.40 4.80

Table 2. Fundamental Properties of Natural and Recycled Aggre-gates

Density(g/cm3)

Absorptionratio (%)

Flat or elongatedparticles in aggregate (%)

Mix I 2.701 0.973 19.91

Mix IV 2.658 2.790 16.78

Fig. 1. Mix Gradation Chart Fig. 2. Air Void Distributions of Cored Mixtures

The Application of Recycled Concrete Aggregate (RCA) for Hot Mix Asphalt (HMA) base Layer Aggregate

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2.4 Marshall TestBecause the Marshall mix design method is still used in many

countries, Marshall tests were performed on specimens with aheight of 65 mm at 25oC according to KS F 2337 and ASTM D1559. As described, the optimal binder content for each mixturewas determined according to the Superpave mix design methodto find any possible relationship between the Marshall mixdesign method and the Superpave mix design method.

2.5 Indirect Tensile Strength TestThe IDT strength test was performed to assess the resistance of

each mixture to cracking according to ASTM D4123-82 and KSF 2382. The test temperature and loading rate were 25oC and 50mm/min, respectively.

2.6 Kim TestThe Kim test was developed to evaluate the rutting resistance

of asphalt mixtures (Doh, 2006; Kim, 2004). As shown in Fig. 3,a rod with a rounded tip contacts a specimen with a height of 63mm and diameter of 100 mm and is moved downward with aloading rate of 30 mm/min. The test temperature was 60±4 m.Eq. (1) represents the relationship for the deformation strength,displacement, and maximum force at failure, as developed byKim (2004).

(1)

where, SD = deformation strength (MPa),P = maximum load (N), andy = deformation (mm).

2.7 Wheel Tracking TestThe wheel tracking test is known to simulate field conditions

more realistically than the other testing methods in terms of rutresistance of asphalt mixtures. As with the Kim test, the testtemperature was set to 60±0.5oC, and the testing was conductedaccording to KS F 2374. The dimension of the mold was 300×300×50 mm, and the asphalt mixture placed in the mold wascompacted using a roller compactor and kneading compactor.The maximum compaction force was 8,820 N, and the contactpressure of the wheel during the test was 628±15 kPa. Theloading wheel moved back and forth from one end of the mold tothe other with a repetition rate of 42 times/minute. The rut depthwas recorded at the center of the asphalt specimen in 15-minuteintervals (0, 15, 30, 45, 60 minutes). Fig. 4 shows the wheeltracking test equipment. It is obvious that the wheel tracking testresults were affected not only by the composition of the asphaltmixtures but also by the initial air void content of the asphaltmixture, the test temperature, and the loading application method.Therefore, without changing the test temperature and the numberof compactions, preliminary test specimens were cut into nine re-ctangular pieces, and the air void content of the center specimenwas measured. This test was repeated for each mix type in orderto estimate the total mass of each mixture, resulting in 5% airvoid at the center of the mixture. Fig. 5 shows the variations inair void content of the total mass, with Mix I as an example.

SD0.32P

10 20y y2–+( )2

---------------------------------------=

Table 3. Absorption Ratio of Mix Types Considered

Mix I Mix II Mix III Mix IV

Absorption Ratio (%) 1.11 2.58 1.63 3.10

Fig. 3. Kim Test

Fig. 4. Wheel Tracking Test

Fig. 5. Determination of Mass of Asphalt Mixtures (Mix I)



2.8 Indirect Tensile Strength Ratio TestThe indirect tensile strength ratio test was performed to predict

the susceptibility of asphalt mixtures to moisture damage, asspecified by ASTM D 4867 and KS F 2398. The loading rate andtesting temperature were 50 mm/minute and 25oC by ASTM D4867 and KS F 2398.

3. Test Results and Discussion

3.1 Marshall TestIn the Marshall mix design method, the Voids in Total Mix

(VTM), Voids in the Mineral Aggregate (VMA), Voids Filledwith Asphalt (VFA), and stability are the four criteria used toevaluate the performance of asphalt mixtures. Considering thevariability in measured values, it is concluded that Mix I and MixII are within the upper and lower limits of these criteria (i.e.,VTM, VMA, VFA, and stability), whereas the values for Mix IVare apparently outside the limits, as shown in Fig. 6. In the caseof Mix III, the measured VMA and stability values satisfy thecriteria, but the VTM and VFA values do not. It appears that thestrength of the coarse aggregate plays an important role underdynamic loading in the Marshall test compaction processbecause Mix III and Mix IV with coarse RCA show lower VTMvalues compared to Mix I and Mix II, respectively, even thoughthis trend was not observed in specimens compacted by thegyratory compactor, as shown in Fig. 7.

Based on these test results, it is concluded that the optimal bindercontents determined from the Superpave mix design method arenot significantly different from those determined from theMarshall mix design method for mixtures with natural coarseaggregate. However, the Marshall mix design method may notbe appropriate to simulate conditions of asphalt mixtures withRCA in the field, because the dynamic loading in the Marshall

test compaction process may cause breaks in coarse RCA and,therefore, cause unexpected results.

3.2 Indirect Tensile Strength TestFig. 7 shows the IDT strength of each mix type. As mentioned,

the specimens used in this test were compacted by the gyratorycompactor. The rank of this test does not match the stabilities inFig. 6(d) and no statistically significant trend was observed as afunction of air void content. However, this result is in the linewith observations made in other studies; that is, it is the bindingstrength of the asphalt binder (i.e., binder type) rather than theaggregate type that has more effect on the tensile strength ofasphalt mixtures.

3.3 Kim TestThe deformation strength of each mix type is presented in Fig.

8. Unlike the indirect tensile strength test, a clear relationshipbetween the deformation strength and air void content can beobserved for all mix types except for Mix III. Although the

Fig. 6. Marshall Test Properties of Mixtures: (a) VTM, (b) VMA, (c) VFA, (d) Stability

Fig. 7. Indirect Tensile Strength Test Results

The Application of Recycled Concrete Aggregate (RCA) for Hot Mix Asphalt (HMA) base Layer Aggregate

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deformation strength of Mix III does not show a decreasingrelationship with air void content, it is not significantly lowerthan that of Mix I and Mix II. Considering that RCA was used ascoarse aggregate in Mix III and Mix IV, it seems that loweraggregate friction, which is caused by RCA, results in the lowerdeformation strength of Mix III and Mix IV. Also, the steeperslopes of Mix I and Mix II support that aggregate friction is animportant feature that affects the deformation strength of asphaltmixtures.

In the case of Mix II, the higher deformation strength seems tobe caused by the combined effect of aggregate friction and ab-sorption ratio, which possibly increases the strength of the naturalcoarse aggregate. However, regardless of its high absorption ratio,Mix IV shows the lowest deformation strength for the entire airvoid ratio, probably due to the low quality of both recycledcoarse aggregate and fine aggregate in terms of strength.

3.4 Wheel Tracking TestFrom the wheel tracking test, it is observed that Mix II has the

highest resistance to rutting. In the case of Mix III, the deforma-tion keeps increasing with relatively low variations in rate as thenumber of loading cycles increases. This observation is similarto that made from the Kim test. In the Kim test, the deformationstrength of Mix II does not vary as the air void content varies.Mix I shows a more rapid increase in deformation, but the

cumulative deformation seen at the end of the test is about thesame as for Mix III. Considering that the air void contents of themixtures are very similar to each other and close to 5.0%, theresistance of these mixtures is ranked in the order (best to worst)of Mix II, Mix III, Mix I, and Mix IV for the given test condi-tions. It is noted that this order agrees well with the results of theKim test at over 5.0% air void content, as shown in Fig. 8.

3.5 Indirect Tensile Strength Ratio TestThe indirect tensile strength ratios of the four mixtures were

determined by dividing the indirect tensile strength ratios of theoriginal specimen by those of moisture-conditioned specimens.The minimum acceptable indirect tensile strength ratio of 0.7 isachieved for all mix types. Fig. 10 shows the indirect tensilestrength ratio of each mix type before and after conditioning.

4. Conclusions

In this study, the performance of asphalt mixtures with RCAare evaluated using the Marshall test, IDT strength test, Kim test,wheel tracking test, and indirect tensile strength ratio test. Theapplicability of the Marshall mix design method to asphaltmixtures with RCA is evaluated as well. Because Mix II and MixIII considered in this study show comparable performance interms of indirect tensile strength ratio, deformation strength, rutdepth, and IDT strength ratio, it is concluded that Mix II and MixIII can be used as base layer aggregates. However, Mix IV, whichconsists of coarse and fine RCA, shows the lowest resistance totensile stress and shear flow and, therefore, this mix is notrecommended to be used as base layer aggregate. By evaluatingthe Marshall test properties of each mixture, it is also concludedthat the dynamic loading in the Marshall test compaction methodpossibly causes friction in the RCA of the asphalt mixtures and,therefore, leads to an underestimation of the engineering proper-ties of HMA with RCA

Acknowledgments

This research was supported by the Chung-Ang UniversityResearch Scholarship Grants in 2008~2009.

Fig. 8. Kim Test Results

Fig. 9. Wheel Tracking Test Results

Fig. 10. Indirect Tensile Strength Ratio Test Results



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Documents

The application of Recycled Concrete Aggregate (RCA) for Hot Mix Asphalt (HMA) base layer aggregate